The present invention relates to a bifilar helical electrode arrangement for the transverse excitation of gaseous laser media. The electrode arrangement comprises a helical anode and a helical cathode which are constucted as extended electrodes exhibiting an appropriate profile or which are occupied with a number of individual electrodes (i.e., the helix can be provided with pin electrodes).
By utilizing the bifilar helical electrode arrangement of the invention, atomic gases, molecular gases, gas mixtures, metal vapors, and even gaseous laser media which display an extremely short-lived upper laser level (e.g., nitrogen) can now be excited to intense laser action by a pulsed transverse gas discharge, the helical electrode structure favoring the creation of a laser beam of circular, symmetrical cross section.
A bifilar helical electrode arrangement for the transverse excitation of a molecular laser is described in U.S. Pat. No. 3,725,735 issued Apr. 3, 1973. In that electrode arrangement, the helical anode, as well as the helical cathode, are covered with numerous pin electrodes spaced therealong. In the aforesaid application, the cathode pins are electrically interconnected outside of the discharge envelope of the laser by means of a helical current bus whereas the anode pins are required to be decoupled by utilizing suitable ballast resistors which serve the additional purpose of limiting the current within each discharge channel and thereby stabilizing the nascent arc. Likewise, the external connecting leads of decoupling resistors are interconnected in a helical anode current bus. Cathode and anode current distributors are usually connected to the high voltage supply necessary for excitation at one point only, preferably the central point. It is important in such known bifilar helical electrode arrangements that the discharge gap of the laser be connected in series with a high voltage switch and the capacitor to be discharged. In addition, this part of electrical discharge circuit commonly exhibits a relatively large inductance caused by the intrinsic inductances of the switch and the capacitance, respectively, and by virtue of the necessarily large area conduction paths.
As a consequence of their construction, prior art bifilar helical electrode arrangements are suitable only for the excitation of easily invertable gases (e.g., carbon dioxide) because of the high inductive discharge circuits causing a relatively low rate of voltage and current rise within the gas discharge. Such easily invertable gases can be excited by a comparatively low rate of current rise because of the long lifetime of the excited laser level. On the other hand, the prior art arrangements are not suited for gaseous laser media in which the lifetime of the excited laser level does not exceed 100 nanoseconds. Laser media of this type have to be excited within an equally short time period in order to effectively generate a population inversion. The best known of such laser media is nitrogen for which the lifetime of the excited laser level is only 40 nanoseconds, a value which is generally recognized as a criterion for a "fast" discharge arrangement.